1. Field of the Invention
This invention relates to the in vivo assessment of toxicity and pharmacokinetics of methylglyoxal and to the curative effect of the pharmaceutical composition on cancer.
2. Description of Related Art
As early as 1913, it was observed that methylglyoxal is converted to d-lactic by a strong and ubiquitous enzyme system. But how methylglyoxal is formed in organisms, and from what precursor(s), was unknown at that time. However, in the 1970s and 1980s, the metabolic pathway for methylglyoxal in different organisms had been established with the isolation, purification and characterization of several enzymes responsible for the formation and breakdown of methylglyoxal. That methylglyoxal is a normal metabolite has been firmly established (for a review, see Ray and Ray, 1998).
The anticancer property of methylglyoxal was also known for a long time. In the early 1960s, Szent-Györgyi et al. proposed that methylglyoxal is a natural growth regulator and can act as an anticancer agent (Együd and Szent-Györgyi, 1966, Együd and Szent-Györgyi, 1968; Szent-Györgyi et al., 1967; Szent-Györgyi, 1979). They also provided strong experimental evidence in support of the hypothesis. When mice were inoculated with ascites sarcoma 180 cells and then treated with methylglyoxal, no tumor developed (Együd and Szent-Györgyi, 1968). At the same time, Apple and Greenberg (1967, 1968) showed remarkable curative effect of methylglyoxal in experiments with mice bearing a wide variety of cancers. Other investigators (Conroy, 1979; Elvin and Slater, 1981) had also observed similar anticancer effect of methylglyoxal.
Együd and Szent-Györgyi (1966) suggested that the anticancer property of methylglyoxal is mediated through the growth inhibitory effect of methylglyoxal, which in turn is due to the inhibition of protein synthesis by methylglyoxal. However, whether there is a qualitative difference in the effect of methylglyoxal between normal and malignant cells had not been systematically investigated. Moreover, very few studies had been done previous to that time with human tissue.
Subsequent studies had indicated that methylglyoxal is tumoricidal. It inhibits both glycolysis and mitochondrial respiration of specifically malignant cells (Ray et al., 1991; Halder et al., 1993; Biswas et al., 1997). With a wide variety of postoperative human tissues and also animal tissues and cells, both normal and malignant, it had been observed that methylglyoxal inhibits mitochondrial respiration (at the level of complex I) and inactivates glyceraldehyde-3-phosphate dehydrogenase of specifically malignant cells (Halder et al., 1993; Ray et al., 1994, 1997a, 1997b; Biswas et al., 1997). These results strongly suggest that these two enzymes are altered specifically in malignant cells.
In contrast to the positive effect of methylglyoxal as referred to above, recent publications on methylglyoxal research overwhelmingly state that methylglyoxal is toxic. Numerous papers have appeared in the literature, which mostly with in vitro studies have shown that methylglyoxal reacts with arginine, lysine and free terminal amino groups in proteins resulting in AGE (advanced glycation end products) formation. The possibilities of many deleterious effects of methylglyoxal in the body have been extrapolated based mostly on these in vitro studies. The notable complications are related to diabetes and cataract formation (Thornalley, 1996; Lee et al., 1999; Morgan et al., 2002; Roberts et al., 2003). Evidence had also been put forward that methylglyoxal is mutagenic (Murata-Kamiya et al., 2000) and induces reactive oxygen species formation (Chan et al., 2005; Chang et al., 2005). Since relatively few in vivo studies with methylglyoxal have been done, it is logical to conceive that many of the purported in vitro toxic effects of methylglyoxal may be overwhelmed by the many countervailing reactions in an intact animal. This consideration especially stems from the reports of significant curative effect of methylglyoxal towards cancer-bearing animals that had been observed and mentioned above. Moreover, in vitro studies with human samples had indicated the inhibitory effect of methylglyoxal on glyceraldehyde-3-phosphate dehydrogenase and mitochondrial complex I of specifically malignant cells. The results of all these studies strongly demand that methylglyoxal alone or in combination with other substances should be tested for the possible efficacy of treating cancer patients. However, it has not been tested until the recent past. On the other hand, methylglyoxal bis-guanylhydrazone, a derivative of methylglyoxal, had undergone clinical trial with limited success (Dunzendorfer et al., 1986; Friedman et al., 1986; Gastaut et al., 1987). A need therefore remains to develop in vivo toxicity assessment techniques to determine the pharmacokinetics of methylglyoxal so that the output of such assessment may be relied on by health care providers to make patient treatment decisions, and a pharmaceutical composition for treating patients for whom methylglyoxal treatment is indicated.